'Harden' in the Bible

so, then, to whom He willeth, He doth kindness, and to whom He willeth, He doth harden.

ye may not harden your hearts, as in the provocation, in the day of the temptation in the wilderness,

in its being said, 'To-day, if His voice ye may hear, ye may not harden your hearts, as in the provocation,'

again He doth limit a certain day, 'To-day,' (in David saying, after so long a time,) as it hath been said, 'To-day, if His voice ye may hear, ye may not harden your hearts,'